ATP provides energy coupling between exergonic (energy producing) and endergonic (energy requiring) reactions. (c).
When ATP is hydrolyzed to ATP + Pi (broken down), it releases a great deal of energy. (Pi just means inorganic phosphate, PO4-)
deltaG of this reaction is about -30 kJ/mol, which means it releases a lot of energy. This is the exergonic reaction.
That energy is used to power energonic reactions, that require energy, and whose delta G values are positive.
You can add together the values from the two coupled reactions to understand how much energy is used or produced overall. One example is the synthesis of glucose and fructose, which gains its energy from the hydrolysis of ATP.
Sucrose + glucose <-> fructose delta G = +27 kJ/mol
ATP + H2O <-> ADP +Pi deltaG = -30 kJ/mol
Sucrose + glucose + ATP <-> fructose + ADP + Pi overall: deltaG = -3kJ/mol
Overall, this coupled reaction releases energy, which makes it favorable in the cell! Process drives normal metabolism.